High pressure seal for a pump system for pumping liquid under high pressure

ABSTRACT

A system for pumping liquid under high pressure includes a housing and a high pressure seal. The housing houses a pump assembly and a chamber assembly that includes a chamber for containing high pressure liquid. The seal separates high pressure area in the chamber assembly from low pressure area in the pump assembly. The seal includes a seal opening that receives a piston that moves axially to increase pressure on the liquid in the chamber; an active sealing area adjacent the chamber; a compressible sealing area adjacent the active sealing area; and a connection channel formed through the compressible sealing area between the seal opening and a leakage space formed between the housing and the high pressure seal. The connection channel conducts the liquid, leaked into the leakage space from the chamber, from the leakage space to the seal opening during operation of the piston, providing lubrication for the piston.

BACKGROUND

In high performance liquid chromatography (HPLC), a mobile phase includes a sample fluid, such as a chemical mixture or a biological mixture, with compounds to be separated. The mobile phase is driven through a stationary phase, such as a chromatographic column containing packing medium, by liquid flow in order to separate different compounds of the sample fluid for subsequent identification. The term compound, as used herein, covers compounds which may include one or more different components. The sample fluid is usually provided at a controlled flow rate (e. g., in the range of microliters to milliliters per minute) and at a high pressure (e.g., 20-100 MPa, 200-1000 bar or even up to 200 MPa, 2000 bar) at which compressibility of the sample fluid becomes noticeable. For example, the sample fluid may include a liquid solvent, pumped by a pump system under high pressure, into which sample(s) are injected. The pump system receives the liquid solvent at a low pressure, such as ambient pressure, and outputs the liquid solvent at the desired high pressure through a pumping operation. After injection of the sample, resulting sample fluid is driven through the chromatographic column by the high pressure liquid flow. Different compounds, each having a different affinity to the packing medium, move through the chromatographic column at different speeds. That is, compounds having greater affinity for the packing medium more slowly through the chromatographic column than compounds having less affinity, resulting in the compounds being separated from one another. As a result of the liquid flow, depending on the physical properties of the stationary phase and the mobile phase, a relatively high pressure drop is generated across the chromatographic column.

The mobile phase with the separated compounds exits the chromatographic column and passes through a detector, which registers and/or identifies molecules of the separated compounds, for example, by spectrophotometric absorbance measurements. A two-dimensional plot of the detector measurements against elution time or volume, known as a chromatogram, may be made to enable identification of the compounds. For example, the chromatogram displays a separate curve feature, or “peak,” for each compound. Efficient separation of the compounds by the chromatographic column is advantageous because it provides for measurements yielding well defined peaks having sharp maxima inflection points and narrow base widths, allowing excellent resolution and reliable identification and quantitation of the mixture constituents.

The pump system may include a hydraulic pump, for example, that drives the mobile phase through the chromatographic column. Due to pressure differential between the high pressure liquid contained in a chamber of the pump and the low pressure environment in which the pump operates, portions of the liquid leak from the high pressure side to the low pressure side of the pump, and/or to the exterior of the pump. A small amount of leakage through the point at which a pump piston enters the chamber may be useful to the extent it provides lubrication for the piston. However, an excessive amount of leakage and/or leakage around an outer surface of a seal positioned where the piston enters the chamber is detrimental to pump operation. For example, such leakage may cause undesirable build-up of radially inward forces on the seal that impedes motion of the piston and excessive seepage of the liquid outside the pump itself. Leakage creeping to peripheral faces of the seal escalate the sealing area and thus (area multiplied by the system pressure) the axial sealing forces within the pump system. Of course, repeated usage of the pump results in wear on the seal and moving parts of the pump, thereby increasing liquid leakage and associated problems. Accordingly, a pump and system and corresponding high pressure seal are needed that reduces and/or efficiently redirects liquid leakage for lubrication purposes.

SUMMARY

In a representative embodiment, a system is provided for pumping liquid under high pressure. The system includes a housing and a high pressure seal. The housing is configured to house a chamber assembly and a pump assembly, the chamber assembly including a chamber for containing a liquid under high pressure. The high pressure seal separates a high pressure area in the chamber assembly from a low pressure area in the pump assembly. The high pressure seal includes a seal opening configured to receive a piston operable by a motor in the pump assembly and configured to move axially within the seal opening to increases pressure on the liquid in the chamber; an active sealing area adjacent the chamber; a compressible sealing area adjacent the active sealing area; and a connection channel formed through a wall of the compressible sealing area between the seal opening and a leakage space formed between the housing and the high pressure seal. The connection channel is configured to conduct the liquid, leaked into the leakage space from the chamber, from the leakage space to the seal opening during operation of the piston. The liquid conducted from the leakage space to the seal opening provides lubrication for the piston as the piston moves axially within the seal opening.

In another representative embodiment, a high pressure seal separates high and low pressure areas in a pump system. The high pressure seal includes an active sealing area, a compressible sealing area, a seal opening, and a connection channel. The active sealing area is adjacent a chamber containing a liquid under high pressure, and the compressible sealing area is adjacent the active sealing area. The seal opening is configured to receive a piston configured to move axially within the seal opening to increase pressure on the liquid in the chamber. The connection channel is formed through the compressible sealing area, and is configured to connect the seal opening and a leakage space formed between a seal engagement surface of a housing containing the high pressure seal and a housing abutment surface of the high pressure seal. A first leakage path enables the liquid to leak directly from the chamber to the seal opening, and a second leakage path enables the liquid to leak from the chamber to the leakage space, and from the leakage space through the connection channel to the seal opening.

BRIEF DESCRIPTION OF THE DRAWINGS

The representative embodiments are best understood from the following detailed description when read with the accompanying drawing figures. Wherever applicable and practical, like reference numerals refer to like elements.

FIG. 1 is a simplified block diagram of a liquid separation system, e.g. used in high performance liquid chromatography (HPLC), according to a representative embodiment.

FIG. 2 is a cross-sectional view of a pump system, including a high pressure seal, according to a representative embodiment.

FIG. 3 is a cut-away view of the high pressure seal shown in FIG. 2 in an undeformed state, according to a representative embodiment.

FIG. 4 is a cross-sectional view of the high pressure seal shown in FIG. 2, positioned within a housing of the pump system, according to a representative embodiment.

DETAILED DESCRIPTION

In the following detailed description, for purposes of explanation and not limitation, illustrative embodiments disclosing specific details are set forth in order to provide a thorough understanding of embodiments according to the present teachings. However, it will be apparent to one having had the benefit of the present disclosure that other embodiments according to the present teachings that depart from the specific details disclosed herein remain within the scope of the appended claims. Moreover, descriptions of well-known devices and methods may be omitted so as not to obscure the description of the example embodiments. Such methods and devices are within the scope of the present teachings.

Generally, it is understood that as used in the specification and appended claims, the terms “a”, “an” and “the” include both singular and plural referents, unless the context clearly dictates otherwise. Thus, for example, “a device” includes one device and plural devices.

As used in the specification and appended claims, and in addition to their ordinary meanings, the terms “substantial” or “substantially” mean to within acceptable limits or degree. For example, “substantially cancelled” means that one skilled in the art would consider the cancellation to be acceptable. As a further example, “substantially removed” means that one skilled in the art would consider the removal to be acceptable.

As used in the specification and the appended claims and in addition to its ordinary meaning, the term “approximately” means to within an acceptable limit or amount to one having ordinary skill in the art. For example, “approximately the same” means that one of ordinary skill in the art would consider the items being compared to be the same.

Various representative embodiments generally provide a connection channel formed through the wall of a high pressure seal in a pump system. The connection channel connects a leakage space, formed between the high pressure seal and a housing containing the high pressure seal, and a seal opening, through which a piston moves axially to increase pressure of a liquid in a chamber adjacent to the high pressure seal. The connection channel enables liquid leaked from the chamber into the leakage space (e.g., due to pressure differential) to be passed to the seal opening, thereby providing lubrication for the piston, and otherwise preventing undesirable changes in axial sealing forces due to enlarging sealing area for the pump system and/or seepage of liquid outside the housing caused by liquid leaked from the chamber.

FIG. 1 is a simplified block diagram of a liquid separation system, e.g. used in high performance liquid chromatography (HPLC), according to a representative embodiment.

Referring to FIG. 1, liquid separation system 100 includes a solvent supply 110, a pump system 120, a sample injector 130, a separating device 140, a detector 150 and a fractionating unit 160. The pump system 120 may be a hydraulic pump, for example, which receives a liquid solvent from the solvent supply 110. The liquid separation system 100 may further include a degasser 115, through which the pump system 120 receives the liquid solvent, where the degasser 115 degases the liquid solvent to reduce the amount of dissolved gases. The pump system 120 is configured to drive the mobile phase through the separating device 140, which may be a chromatographic column that includes a stationary phase, for example. The sample injector 130, provided between the pump system 120 and the separating device 140, introduces portions of one or more sample fluids into the flow of the mobile phase downstream from the pump system 120. The stationary phase of the separating device 140 is adapted for separating compounds of the sample fluid. For example, when a chromatographic column may include a stainless steel tube defining a bore that contains a packing medium as the stationary phase. The packing medium may be silane derivatized silica spheres, for example, having a diameters between 0.5 to 50 μm, or 1 to 10 μm or even 1 to 7 μm, packed under pressure in uniform layers that ensure a uniform flow of the transport liquid and the sample through the chromatographic column to promote effective separation of the sample constituents. The detector 150 detects separated compounds of the sample fluid, and the fractionating unit 160 outputs the separated compounds.

As mentioned above, the pump system 120 receives the liquid solvent at a low pressure (e.g., ambient pressure) and outputs the liquid solvent at a high pressure by virtue of the pumping operation, for driving the mobile phase (with injected samples) through the separating device 140 at the high pressure. The mobile phase may include one solvent only, or a mixture of multiple solvents. When the mobile phase includes multiple solvents, the solvents may be mixed at the low pressure provided upstream of the pump system 120, so that the pump system 120 receives and pumps the already mixed solvents as the mobile phase. Alternatively, the pump system 120 may include multiple individual pumping units (not shown in the depicted embodiment), which receive and pump different solvents such that the mixing of the mobile phase (as received by the separating device 140) occurs at high pressure downstream of the pump system 120. The mixture of solvents in the mobile phase may be constant over time (referred to as “isocratic mode”) or varied over time (referred to as “gradient mode”).

The liquid separation system 100 further includes a processing unit 170 coupled to one or more of the devices in the liquid separation system 100, indicated in FIG. 1 by dashed arrows. Any type of wired and/or wireless connections between the processing unit 170 and these devices may be incorporated to enable transmission of control signals and/or reception of data, without departing from the scope of the present teachings. Generally, the processing unit 170 may be implemented by a computer processor (e.g., of a PC or dedicated workstation), application specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or combinations thereof, using software, firmware, hard-wired logic circuits, or combinations thereof. A computer processor, in particular, may be constructed of any combination of hardware, firmware or software architectures, and may include memory (e.g., volatile and/or nonvolatile memory) for storing executable software/firmware executable code that allows it to perform the various functions. In an embodiment, the computer processor may comprise a central processing unit (CPU), for example, executing an operating system. The processing unit 170 may include a storage device, such as random access memory (RAM), read-only memory (ROM), flash memory, electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), hard disk drive (HDD), or the like. A user interface, such as a graphical user interface (GUI) may be included with the processing unit 170 for a user to control operations and/or view data and computation results of the liquid separation system 100.

As mentioned above, the processing unit 170 may be configured to receive data and other information and/or to control respective operations of the devices in the liquid separation system 100. For example, the processing unit 170 may control operation of the pump system 120 (e.g. setting control parameters) and receive information regarding actual working conditions (such as output pressure, flow rate, etc. at an outlet of the pump). The processing unit 170 may also control operation of the solvent supply 110 (e.g. monitoring the level or amount of the solvent available) and/or the degasser 115 (e.g. setting control parameters such as vacuum level) and may receive information regarding actual working conditions (such as solvent composition supplied over time, flow rate, vacuum level, etc.). The processing unit 170 might further control operation of the sample injector 130 (e.g. controlling sample introduction or synchronization of the sample introduction with operating conditions of the pump system 120). The separating device 140 may also be controlled by the processing unit 170 (e.g. selecting a specific flow path or column, setting operation temperature, etc.), and send—in return—information (e.g. operating conditions) to the processing unit 170. Accordingly, the detector 150 might be controlled by the processing unit 170 (e.g. with respect to spectral or wavelength settings, setting time constants, start/stop data acquisition), and send information (e.g. about the detected sample compounds) to the processing unit 170. The processing unit 170 might also control operation of the fractionating unit 160 (e.g. in conjunction with data received from the detector 150) and provides data back. Finally the data processing unit might also process the data received from the system or its part and evaluate it in order to represent it in adequate form prepared for further interpretation.

FIG. 2 is a cross-sectional view of a pump system, including a high pressure seal, according to a representative embodiment.

Referring to FIG. 2, pump system 200 may be incorporated for use as pump system 120, shown in FIG. 1, for example. The pump system 200 includes a housing 210 that contains a chamber assembly 214 and a pump assembly 215 to which the chamber assembly 214 is connected. The pump assembly 215 includes a motor (not shown) and spindle assembly (not shown) for driving a piston 218 in an axial direction through cylinder 217 for pumping the liquid solvent through chamber 220 at a high pressure (e.g., about 20-100 MPa, 200-1000 bar, or beyond up to 200 MPa, 2000 bar). The piston 218 may have a cylindrical shape that fits concentrically within the cylinder 217, such that an outer surface 219 of the piston 218 is able to slide along an inner surface of the cylinder 217.

The chamber assembly 214 includes inlet bore 221 to the chamber 220 for receiving liquid at low pressure, e.g., from the solvent supply 110. The received liquid is compressed within the chamber 220, such that the chamber 220 contains liquid under high pressure. The high pressure liquid is discharged from the chamber 220 through outlet bore 222 at the high pressure, e.g., to the separating device 140. The inlet bore 221 and the outlet bore 222 may include inlet and outlet ball valves (not shown) for providing inlet and outlet valves, respectively. The piston 218 moves axially through the cylinder 217 in and out of the chamber 220. While moving out of the chamber 220, the inlet valve opens for sucking liquid into the chamber 220 through the inlet bore 221 and the outlet valve blocks the compressed liquid from flowing back into the chamber 220 through the outlet bore 222. While moving into the chamber the inlet valve blocks the inlet bore 221 to prevent loss of liquid and the outlet valve opens to pass the displaced liquid of the decreasing chamber volume through the outlet bore 222.

A high pressure seal 230 is positioned within the housing 210 between the chamber assembly 214 and the pump assembly 215 to minimize and/or redirect leakage of liquid from the high pressure chamber 220 during the pumping operation. The high pressure seal 230 abuts the housing 210 in the chamber assembly 214 on a high pressure area 214′ of the pump system 200, and abuts a cap 240 and a cap ring 250 in the pump assembly 215 on a low pressure area 215′ of the pump system 200. In the depicted embodiment, the cap 240 is contained within the housing 210, and the cap ring 250 is contained within the cap 240. More particularly, a housing abutment surface 231 of the high pressure seal 230 abuts a seal engagement surface 211 of the housing 210 in the chamber assembly 214. A cap abutment surface 232 of the high pressure seal 230 abuts a seal engagement surface 241 of the cap 240, and a ring abutment surface 233 of the high pressure seal 230 abuts a seal engagement surface 251 of the cap ring 250, positioned within the housing 210 in the pump assembly 215. The high pressure seal 230 thereby separates the high pressure area 214′ in the chamber assembly 214 from the low pressure area 215′ (e.g., ambient pressure) in the pump assembly 215.

The high pressure seal 230 includes a seal opening 234, the cap 240 includes a cap opening 244, and the cap ring 250 includes a cap ring opening 254, all of which are aligned with one another to form corresponding portions of the cylinder 217 to receive the piston 218. Misalignment may cause extreme wear of moving components and may alter the shape of components not designed for high pressure. In an embodiment, a clearance between the cap ring opening 254 and the piston 218 is tight enough to prevent contact between the cap opening 244 and the outer surface 219 of the piston 218 while operating.

As mentioned above, the piston 218 is guided within the high pressure seal 230 at the chamber assembly 214 and at the pump assembly 215 at the opposite side for reciprocating movement along and/or rotation around a longitudinal axis. That is, the piston 218 moves into and out of the chamber 220, pressurizing the liquid contained therein and pumping the high pressure liquid out of the outlet bore 222, by sliding back and fourth axially (including through the seal opening 234, the cap opening 244 and the cap ring opening 254). The surface of the seal opening 234, in particular, engages the outer surface 219 of the piston 218 to substantially prevent liquid from escaping the chamber 220, although some liquid leakage does occur, as discussed below, which serves as lubricant for the piston 218.

FIG. 3 is a cut-away view of the high pressure seal 230 shown in FIG. 2, according to a representative embodiment.

Referring to FIG. 3, the high pressure seal 230 includes an active sealing area 310 adjacent the chamber 220 (not shown in FIG. 3) and a compressible sealing area 330 adjacent the active sealing area 310. The seal opening 234 is formed through both the active sealing area 310 and the compressible sealing area 330. As mentioned above, the seal opening 234 is aligned with the cap opening 244 and the cap ring opening 254 to form a portion of the cylinder 217 (which may be a kind of skin with a common axis where the involved parts abut), accommodating axial movement of the piston 218.

The active sealing area 310 is hydraulically supported, and defines a circumferential spring channel 312 that contains a spring 314. The active sealing area 310 may be formed of an elastomeric material, such as mainly polymers, PTFE, PE and the like, which fulfill inertness requirements of the pumped liquids, for example. The spring 314 exerts a radially inward force on the outer surface 219 of the piston 218 (which passes through seal opening 234) and a radially outward force on a seal engagement surface 211 of the housing 210 to enhance and otherwise facilitate the sealing effect between the seal engagement surface 211 and the housing abutment surface 231 of the high pressure seal 230 upon axial compression of the high pressure seal 230 and thus radial expansion against the seal engagement surface 211. During operation of the piston 218, high pressure liquid from the chamber 220 leaks into the leakage space 340 formed between the housing abutment surface 231 of the high pressure seal 230 and the seal engagement surface 211 of the housing 210 and into the seal opening 234 around the piston 218. The radially inward and outward forces reduces the leakage of high pressure liquid into the leakage space 340 and the seal opening 234, although some leakage is desirable in order to provide lubrication between the outer surface 219 of the piston 218 and an inner surface of the cylinder 217 (including the seal opening 234). The radially outward force reduces the leakage of the high pressure liquid into the leakage space 340. With increasing pressure within the chamber 220 and thus within the spring channel 312, the forces of the spring 314 become negligible since the liquid pressure itself provides the inward and outward forces by means of hydraulic support.

The compressible sealing area 330 is positioned between the active sealing area 310 and the cap 240 and/or the cap ring 250. The compressible sealing area 330 may be formed of the same material as the active sealing area 310, and may even be a portion of a common part, where the active sealing area 310 and compressible sealing area 330 serve different functions. Alternatively, the active and compressible sealing areas 310 and 330 may be a composite of different merged materials forming the high pressure seal 230. In the latter case, the polymer for the compressible sealing area 330 would be chosen to a polymer with higher strength than that of the active sealing area 310. Generally, the compressible sealing area 330 may compress axially under pressure against the cap 240 and/or the cap ring 250, holding the high pressure seal 230 in position between the chamber 220 and the pump assembly 215.

In an embodiment, hydraulic resistance of the high pressure seal 230 is adjustable. For example, the hydraulic resistance of the high pressure seal may be adjusted to decrease pressure in the compressible sealing area 330 to between about 1 percent and about 60 percent of pressure in the high pressure area 214′. The drop in pressure may be due to a cross sectional geometry of the connection channel 333 (e.g., where the pressure difference may be the diameter of the connection channel 333 to a power of four). Also, the drop in pressure may be due to the number of connection channels 333, where there are more than one connection channel 333 (e.g., up to 100 or more). Supports or porous fillings of the connection channel(s) 333, such as a kind of stand for the connection channel 333 which changes the hydraulic resistance, may also cause the drop in pressure. Porous connections between the active sealing area 310 and the compressible sealing area 330 may cause the drop in pressure as well. In the latter case, the active and compressible sealing areas 310 and 330 may be formed of two different materials, as mentioned above.

The compressible sealing area 330 includes an axial fixing portion 331 configured to attach the high pressure seal 230 to the housing 210. In embodiments with exchangeable seals, the axial fixing portion 331 may be used to attach the high pressure seal 230 to the cap 240 and/or the cap ring 250, in addition to or instead of attaching to the housing 210. The compressible sealing area 330 may be attached using any means of attachment, such as screws, rivets, plugs and other physical connectors. An example of a sealing attachment is discussed below with reference to FIG. 4.

In addition, a connection channel 333 is formed through a wall 334 of the compressible sealing area 330. The connection channel 333 is configured to conduct leaked liquid collected in the leakage space 340 into the seal opening 234, where it serves as additional lubricant for the piston 218. The liquid leakage that collects in the leakage space 340 is caused by the pressure differential between the high pressure area 214′ and the low pressure area 215′, and operation of the piston 218, as discussed above. In various embodiments, the connection channel 333 may have a cylindrical shape with a diameter between about 20 μm and about 400 μm, for example. Also, although one connection channel 333 is depicted in FIG. 3, it is understood that multiple connection channels 333 may be formed through the compressible sealing area 330, as mentioned above, extending radially from the seal opening 234 to the leakage space 340, without departing from the scope of the present teachings. The size and/or number of connection channel(s) 333 may vary in order to accommodate transfer of various volumes of liquid leakage, without departing from the scope of the present teachings.

FIG. 4 is a cross-sectional view of the high pressure seal 230 shown in FIG. 2, positioned within housing 210 of the pump system 200, according to a representative embodiment.

Referring to FIG. 4, the high pressure seal 230 is shown in a substantially compressed state with the piston 218 positioned within the seal opening 234. As discussed above, the active sealing area 310 adjoins the chamber 220, and the compressible sealing area 330 is positioned between the active sealing area 310 and the cap ring 250/cap 240. The high pressure seal 230 is held in place by the confines of the housing 210, e.g., by contact between the seal engagement surface 211 of the housing 210 and the housing abutment surface 231 of the high pressure seal 230. The high pressure seal 230 is further secured to the housing by the connections and/or sealing attachments on the axial fixing portion 331. For example, in the depicted embodiment, the axial fixing portion 331 includes a circumferential protrusion 332 configured to press into a circumferential recess 213 formed in the housing 210 when the high pressure seal 230 is compressed, forming an additional sealing barrier, which may border the leakage space 340. Of course, other types of physical attachment between the high pressure seal 230 and the housing 210 (as well as the cap 240 and/or the cap ring 250) may be incorporated without departing from the scope of the present teachings.

As discussed above with reference to FIG. 3, the high pressure seal 230 includes the active sealing area 310 and the compressible sealing area 330. The active sealing area 310 includes the spring channel 312 for containing the spring 314, which exerts a radially inward force on the outer surface 219 of the piston 218 and a radially outward force on the seal engagement surface 211 of the housing 210. The compressible sealing area 330 is positioned between the active sealing area 310 and the cap ring 250 and the cap 240. The compressible sealing area 330 includes the connection channel 333, formed through wall 334, for conducting leaked liquid collected in the leakage space 340 into the seal opening 234. The compressible sealing area 330 may compress axially and expand radially as a pressure differential between the high pressure area 214′ in the chamber assembly 214 and the low pressure area 215′ in the pump assembly 215 increases.

According to the depicted embodiment, the high pressure liquid contained in the chamber 220 that leaks during operation of the piston 218 (and therefore not discharged from the outlet bore 222) follows two general leakage paths from the chamber 220 to the seal opening 234: representative first leakage path 351 and second leakage path 352 (indicated by dashed arrows). The first leakage path 351 is a direct leakage path, where high pressure liquid leaks directly from the chamber 220 into the seal opening 234 through a space between an inner diameter of the active sealing area 310 and the outer surface 219 of the piston 218. The leakage results from the axial movement of the piston 218 and towing losses between the high pressure area 214′ and the low pressure area 215′, and is a known part of the described sealing principle. (The piston 218 is radially depressing the spring channel 312, which otherwise would extend into the seal opening 234.) Towing losses occur due to a decreasing gap between the outer surface 219 and the high pressure seal 230 (e.g., housing abutment surface 231) in the direction of movement of the piston 218 (from the high pressure area 214′ to the active sealing area 310). Adhesive bonded liquid generates an additional pressure (“towing pressure”) within the gap, which tends to cause the liquid to undercut the active sealing area 310, resulting in the towing loss.

The second leakage path 352 is an indirect leakage path and results from very small axial movements between the housing abutment surface 231 of the seal and the seal engagement surface 211 of the housing following the movement of the piston. Following the second leakage path 352, the high pressure liquid leaks from the chamber 220 into the leakage space 340 (formed circumferentially around the high pressure seal 230 between the housing abutment surface 231 and the seal engagement surface 211), passes from the leakage space 340 through the connection channel 333 to the seal opening 234, and is forced into the seal opening 234 through a space between an inner diameter of the compressible sealing area 330 and the outer surface 219 of the piston 218. As used in this context, “space” refers more to a possible liquid path when pressure drops, rather than an existing hollow area, for example, since the high pressure seal 230 under compression is extruded, thus tending to fill surrounding gaps, such as the axial space in front of the active sealing area 310 along of the seal engagement surface 211, due to the elasticity and/or ductility of the high pressure seal 230.

In both the first leakage path 351 and the second leakage path 352, the leaked liquid moves in a direction from the high pressure area 214′ to the low pressure area 215′ of the pump system 120. The leaked liquid from the first and second leakage paths 351 and 352 merge into a combined leakage path 356, providing lubrication for the piston 218 moving through the compressible sealing area 330.

One of ordinary skill in the art appreciates that many variations that are in accordance with the present teachings are possible and remain within the scope of the appended claims. These and other variations would become clear to one of ordinary skill in the art after inspection of the specification, drawings and claims herein. The invention therefore is not to be restricted except within the spirit and scope of the appended claims. 

What is claimed is:
 1. A system for pumping liquid under high pressure, the system comprising: a housing configured to house a chamber assembly and a pump assembly, the chamber assembly comprising a chamber for containing a liquid under high pressure; a high pressure seal separating a high pressure area in the chamber assembly from a low pressure area in the pump assembly, the high pressure seal comprising: a seal opening configured to receive a piston operable by the pump assembly and configured to move axially within the seal opening to increases pressure on the liquid in the chamber; an active sealing area adjacent the chamber; a compressible sealing area adjacent the active sealing area; and a connection channel formed through a wall of the compressible sealing area between the seal opening and a leakage space formed between the housing and the high pressure seal, the connection channel being configured to conduct the liquid, leaked into the leakage space from the chamber, from the leakage space to the seal opening during operation of the piston, wherein the liquid conducted from the leakage space to the seal opening provides lubrication for the piston as the piston moves axially within the seal opening.
 2. The system of claim 1, wherein the high pressure seal further comprises: an axial fixing portion configured to attach the high pressure seal to the housing.
 3. The system of claim 1, wherein the compressible sealing area is formed of an elastomeric material.
 4. The system of claim 3, wherein the compressible sealing area compresses axially and expands radially as a pressure differential between the high pressure area in the chamber assembly and the low pressure area in the pump assembly increases.
 5. The system of claim 3, wherein active sealing area is hydraulically supported.
 6. The system of claim 5, wherein active sealing area defines a circumferential spring channel that contains a spring for exerting a radially inward force on the piston in the seal opening and a radially outward force on the housing to enhance sealing of the seal.
 7. The system of claim 5, wherein hydraulic resistance of the high pressure seal is adjustable.
 8. The system of claim 7, wherein the hydraulic resistance of the high pressure seal is adjustable to between about 1 percent and about 60 percent of pressure in the high pressure area.
 9. The system of claim 8, wherein the hydraulic resistance of the high pressure seal is adjustable due to a cross sectional geometry of the connection channel.
 10. The system of claim 8, wherein the hydraulic resistance of the high pressure seal is adjustable due to a number of connection channels.
 11. The system of claim 8, wherein the hydraulic resistance of the high pressure seal is adjustable due to supports or porous fillings of the connection channel.
 12. The system of claim 8, wherein the hydraulic resistance of the high pressure seal is adjustable due to a porous connection between the active sealing area and the compressible sealing area.
 13. The system of claim 1, wherein the low pressure area is substantially ambient pressure.
 14. The system of claim 1, further comprising: a cap contained within the housing in the pump assembly; and a cap ring contained within the cap, the cap ring being adjacent the compressible sealing area, wherein the compressible sealing area compresses axially against at least the cap ring, holding the high pressure seal in position between the chamber and the pump assembly.
 15. The system of claim 14, wherein the cap defines a cap opening and the cap ring defines a cap ring opening, each of the cap opening and the cap ring opening being aligned with the seal opening and configured to receive the piston, and wherein a clearance between the cap ring opening and the piston is tight enough to prevent contact between the cap opening and an outer surface of the piston while operating.
 16. The system of claim 1, wherein liquid also leaks from the chamber directly into the seal opening during operation of the piston.
 17. A high pressure seal separating high and low pressure areas in a pump system, the high pressure seal comprising: an active sealing area adjacent a chamber containing a liquid under high pressure; a compressible sealing area adjacent the active sealing area; a seal opening configured to receive a piston configured to move axially within the seal opening to increases pressure on the liquid in the chamber; and a connection channel formed through the compressible sealing area, the connection channel being configured to connect the seal opening and a leakage space formed between a seal engagement surface of a housing containing the high pressure seal and a housing abutment surface of the high pressure seal, wherein a first leakage path enables the liquid to leak directly from the chamber to the seal opening, and wherein a second leakage path enables the liquid to leak from the chamber to the leakage space, and from the leakage space through the connection channel to the seal opening.
 18. The seal of claim 17, wherein the liquid from the first and second leakage paths provides lubrication for the piston as the piston moves axially within the seal opening.
 19. The seal of claim 17, wherein the high pressure seal further comprises: an axial fixing portion configured to provide a sealing attachment between the high pressure seal and the housing.
 20. The seal of claim 17, wherein the active sealing area defines a circumferential spring channel that contains a spring for exerting a radially inward force on a surface of the piston in the seal opening and a radially outward force on the seal engagement surface of the housing to enhance sealing. 